The invention relates to a fill level measurement apparatus for measuring a fill level of a fill material in a container. The apparatus includes a housing, which is to be secured to the container by means of a securing device, and a probe to be inserted into the container.
Examples of the type of fill level measurement apparatus to which this invention relates are those working with electromagnetic signals. The signals in these apparatuses are transferred onto at least one probe inserted into the container. The probe serves as a wave guide. It leads the signals into the container and brings the signals reflected from a surface of the fill material back out. The travel time, for example, of the electromagnetic signals can be determined, and, from that, the fill level is established.
An electronic circuit for producing electromagnetic signals, as well as a receiver- and evaluation-circuit for determining a fill level, are described e.g. in EP-A 780 665.
Suited to serve as the wave guide are e.g. bare metal wires, also termed xe2x80x9cSommerfeld wave guidesxe2x80x9d, or insulated metal wires. These last are also known under the designation xe2x80x9cGoubau wave guidesxe2x80x9d.
Further examples of the type of fill level measurement apparatus to which this invention relates are capacitive fill level measurement apparatuses. In this case, the probe forms a capacitor with a wall of the container, and its capacity depends on the instantaneous fill level. Usually, the capacity is registered by means of a measurement circuit, and this is converted into a fill level dependent measurement signal.
Fill level measurement apparatuses of these types are used in a multiplicity of applications, both in the storage of materials and in the processing industry, e.g. in the chemical, food and oil industries.
For installing and removing conventional fill level measurement apparatuses, housing and probe are moved, typically screwed, relative to a container opening, through which the probe is to be placed in the container. Because of their small space requirements, the securing devices preferably used are screw-in threads provided on the housing, by means of which the housings are screwed into threaded nozzles on the container.
When removing such fill level measurement apparatuses, especially in the case of bulk goods containers, there is often the problem that the probe is at least partially covered by the fill material when the container is not completely emptied, and the fill material interferes with a free movement, especially a rotation, of the probe.
When installing, the probe placed in the container first rests against the fill material. A rotational movement of the probe required for securing the housing can lead to a twisting or entanglement of the cable and, in worst cases, even to knots in the cable.
The forenamed problems can certainly be avoided by emptying the container for every installing or removing of such a fill level measurement apparatus. This is, however, itself very expensive and leads, in some cases, to considerable extra costs, e.g. when a manufacturing process then has to be interrupted for some time.
EP-A 0 924 792 discloses a fill level measurement apparatus for measuring a fill level of a fill material in a container, which apparatus includes:
a housing having a first section and a second section,
whose sections each have a central, axial bore,
wherein the first section has a smaller inner diameter than the second section, and
a securing device provided on the housing for securing the fill level measurement apparatus on the container.
The measurement apparatus in such case uses microwaves to measure fill level. The fill level measurement apparatus radiates microwaves into the container by means of an antenna extending into the container and arranged higher than a highest fill level to be measured. The microwaves are then reflected at the surface of the fill material and received by means of the antenna. The antenna is rotatably inserted into the housing and protrudes through the housing into the container. It is supported rotatably on a terrace surface between the first and second sections. The antenna is secured by a spring washer contacting a container-far annular surface of the antenna. The washer, in turn, is fixed by means of a snap ring entering into a groove in the housing. The end result is that the antenna can still be turned in the housing into a desired position, even after mounting of the housing on the container.
It is an object of the invention to provide a fill level measurement apparatus for measuring the fill level of a fill material in a container by means of a probe inserted into the container, in which the installing and removing of the fill level measurement apparatus can occur without requiring a movement of the probe in the container.
For this, the invention provides a fill level measurement apparatus for measuring a fill level of a fill material in a container, which includes:
a housing having a first section and a second section,
which sections each have a central, axial bore,
wherein the first section has a smaller inner diameter than the second section,
a securing device provided on the housing for securing the fill level measurement apparatus on the container,
an insert arranged in the housing rotatably relative to the housing,
which is supported rotatably on a terrace surface between the first and second sections,
a probe extending into the container, and
a connecting element,
which connects the insert and the probe along an extension of a longitudinal axis of the probe.
In a further development of the invention, the connecting element is a threaded rod screwed into the insert, and the probe is screwed onto an end of the threaded rod extending through the first section.
In a still further development of the invention, a seal is arranged between a second-section-far end of the first section and the probe.
In a still further development, the seal exhibits a conical, outer, lateral surface, with which it contacts an inner, lateral surface of the first section of the housing rotatably relative to the housing about a longitudinal axis of the probe.
In a still further development of the invention, the seal exhibits a conical, inner, lateral surface, which contacts an outer, lateral surface of the probe and by way of which the seal is pressed in the direction of the second section when the probe is screwed in.
In a still further development of the invention, the seal is a ring with doubly conical cross section.
In a still further development of the invention, the seal exhibits internally and/or externally an annular, encircling groove, in which an additional sealing element is located.
In a still further development, the additional sealing element is a shaft seal.
In a still further development of the invention, the probe in operation is fed with electromagnetic signals, which move along the probe to the fill material surface, are reflected there, and then received, and whose travel time is a measure for the instantaneous fill level.
In another development, the probe forms together with a wall of the container a capacitor, whose capacity depends on the instantaneous fill level and in operation is registered by means of a measurement circuit and transformed into a fill level dependent measurement signal.
In a still further development, a fixing of the probe is possible with a clamping pin, which protrudes through an opening in a wall of the second section into a recess in the insert.
The invention and its advantages are explained in further detail on the basis of the figures of the drawing, in which an example of an embodiment is presented; in the figures, equal elements are given the same reference symbols.